A second stage regulator of scuba diving apparatus includes a demand valve for supplying breathable gases to the diver, a diaphragm for sensing the inhalations of the diver, or his demand for breathable gases, and a linkage between the diaphragm and the demand valve for opening the valve in response to demand. The demand valve includes some resilient sealing element, such as an O-ring, a disc, a frusto-conical plug or the like. The resilient sealing element is urged to close by a spring, the power of which must be overcome by the inhalation force acting on the diaphragm. When the apparatus is stored, the sealing element is constantly pressed against the seat. Consequently, there is a substantial possibility that the sealing element will take on a compression set, that is, a loss of resilience and a consequent diminished ability to seal. Incomplete closure results in the loss of precious breathable gases. Frequent replacement of the sealing element is required.
The primary object of the present invention is to provide a simple means for prolonging the useful life of a sealing element of a demand regulator.